In recent years, the CMOS (Complimentary Metal Oxide Semiconductor) image sensor has attracted attention as an image sensor in place of CCD.
This is because the CMOS image sensor has overcome the following problems.
That is, a special process is needed for the production of CCD pixels, a plurality of power supply voltages is needed for the operation thereof, and further, a plurality of peripheral ICs needs to be combined for operation.
The CMOS sensor has overcome several problems such as a system being very complicated for CCD.
For the CMOS image sensor, a manufacturing process similar to that of a general CMOS-type integrated circuit can be used for the manufacture thereof, a single power supply is enough for driving, and further an analog circuit or logical circuit using a CMOS process can be mixed in the same chip.
Thus, the CMOS image sensor has a plurality of big advantages such as being able to reduce the number of peripheral ICs.
The above-described CMOS image sensor (hereinafter, the CMOS image sensor) is widely used in imaging devices such as digital cameras, camcorders, monitoring cameras, and on-vehicle cameras as an image sensor.
The mainstream output circuit of CCD is 1-channel (ch) output using an FD amplifier having a floating diffusion (FD) layer.
In contrast, the CMOS image sensor has an FD amplifier for each pixel and the mainstream output thereof is a column-parallel output type in which a row in an image array is selected and the row is read simultaneously in a column direction.
This is because it is difficult to obtain sufficient driving capabilities from an FD amplifier arranged in a pixel and the data rate needs to be lowered, which makes parallel processing advantageous.
A vast variety of signal output circuits of the column-parallel output type CMOS image sensor has been proposed. One such proposal is a type that includes an analog-digital conversion device (hereinafter, abbreviated as ADC (Analog digital converter)) for each column and captures a pixel signal as a digital signal.
A CMOS image sensor mounted with column-parallel type ADC is disclosed by Non-Patent Literature 1 and Patent Literature 1.
In addition, to realize high-precision AD conversion, a CMOS image sensor using a ΔΣ modulator is proposed (see, for example, Patent Literature 2 or Non-Patent Literature 2).